Hello friend, thank you for rescuing this lucky kitten, it is beautiful, it is surely the smallest of the litter, I recommend that you deworm it or if you can take it to the vet to check it, when they are so withdrawn it may be because of parasites that are transmitted by the mother and also how you found her on the street, we do not know what she may or may not have eaten.
It is important when rescuing a cat from the street to allow time for adaptation and human care.

Thanks for rescuing a cat life ... by the way I am more doggy than cat but I love you.